• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.5-16
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• 2004

This paper presents the modeling of geosynthetic-reinforced compacted soils and discusses the reinforcement effect arising from confining the dilatancy deformation of the soil by geosynthetics. A series of compressive shear tests for compacted sandy soil specimens wrapped by geosynthetics are carried out by quantitatively examining the geosynthetic-reinforcement effect, occurring from a confinement of the dilative deformation in compacted soils during shearing. In the test, the initial degree of compaction is changed for each series of sandy soil specimens so that each series has different degree of dilatancy characteristics. Herein, the axial forces working on the geosynthetics so as to prevent dilative deformation of compacted soils during shearing are measured. Furthermore, the elasto-plastic modeling of compacted soils and a rational determination procedure for input parameters needed in the elasto-plastic modeling are presented. And to describe the irreversible deformation characteristics of compacted soils during shearing, the subloading yielding surface (Hashiguchi (1989)) to the elasto-plastic modeling is introduced. Finally, the elasto-plastic finite element simulation is carried out and the geosynthetic-reinforcement effect is discussed.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.37-46
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• 2004

This paper presents the modeling of geosynthetic-reinforced soils and discusses the reinforcement effect arising from confining the dilatancy deformation of the soil by geosynthetics. A series of compressive shear tests for compacted sandy soil specimens wrapped by geosynthetics are carried out by quantitatively examining the geosynthetic-reinforcement effect, and it occurred from the confinement of the dilative deformation of compacted soils during shearing. In the test, the initial degree of compaction is changed for each series of sandy soil specimens so that each series has different degree of dilatancy characteristics. Herein, the axial forces working to the geosynthetics so as to prevent dilative deformation of compacted soils during shearing are measured. Furthermore, the elasto-plastic modeling of compacted soils and a rational determination procedure of input parameters needed in the elasto-plastic modeling are presented. In this paper, the subloading yielding surface(Hashiguchi(1989)) is introduced to the elasto-plastic modeling which could describe the irreversible deformation characteristics of compacted soils during shearing. Finally, the elasto-plastic finite element simulation is carried out and the geosynthetic-reinforcement effect is discussed.

• Structural Engineering and Mechanics
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• v.85 no.1
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• pp.105-118
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• 2023

The present work is an attempt to develop a simple and accurate finite element formulation for the assessment of thermal shock/thermally induced vibrations in pretwisted and tapered functionally graded material thin (FGM) blades obtained from Voigt and local representative volume elements (LRVE) homogenization models, based on neutral surface approach. The neutral surface of the FGM blade does not coincide with its mid-surface. A finite element model (FEM) is developed using first-order shear deformation theory (FSDT) and the FGM turbine blade is modelled according to the shallow shell theory. The top and the bottom layers of the FGM blade are made of pure ceramic and pure metal, respectively and temperature-dependent material properties are functionally graded in the thickness direction, the position of the neutral surface also depends on the temperature. The material properties are estimated according to two different homogenization models viz., Voigt or LRVE. The top layer of the FGM blade is subjected to high temperature and the bottom surface is either thermally insulated or kept at room temperature. The solution of the nonlinear profile of the temperature in the thickness direction is obtained from the Fourier law of heat conduction in the unsteady state. The results obtained from the present FEM are compared with the benchmark examples. Next, the effect of angle of twist, intensity of thermal shock, variable chord and span and volume fraction index on the transient response due to thermal shock obtained from the two homogenization models viz., Voigt and LRVE scheme is investigated. It is shown that there can be a significant difference in the transient response calculated by the two homogenization models for a particular set of material and geometric parameters.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.1-7
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• 2015

Self-piercing riveting (SPR) process is gaining popularity due to its many advantages. The SPR does not require a pre-drilled hole and has capability to join a wide range of similar or dissimilar materials and combinations of materials. This study investigated the fatigue strength of self-piercing rivet joint with aluminum alloy (Al-5052) and steel (SPCC) sheets. Static and fatigue tests on tensile-shear specimens were conducted. From the static strength aspect, the optimal punching force for the specimen with upper SPCC (U.S) sheet and lower aluminum alloy(L.A) sheets was 34 kN. During static test the specimens fractured in pull-out fracture mode due to influence of plastic deformation of joining area. There was a relationship between applied load amplitude $P_{amp}$ and number of cycles N ; $P_{amp}=19588N_f^{-0.211}$ and $P_{amp}=4885N_f^{-0.083}$ for U.S-L.A and U.A-L.S specimens, respectively. U.A-L.S fatigue specimens failed due to fretting crack initiation around the rivet neck between upper and lower sheets.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.72-85
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• 2000

Rock is a very complex and heterogeneous material, containing structural flaws due to geologic generation process. Because of those structural flaws, deformation and failure of rock when subjected to differential compressive stresses is non-linear. To simulate the non-linear behavior of rock, mechanical crack models, that is, sliding and shear crack models have been used in several studies. In those studies, non-linear stress-strain curves and various behaviors of rock including the changes of effective elastic moduli ($E_1$, $E_2$, ${\nu}_1$, ${\nu}_2$, $G_2$) due to crack growth were simulated (Kemeny, 1993; Jeon, 1996, 1998). Most of the studies have mainly focused on the verification of the mechanical crack model with relatively less attempt to apply it to practical purposes such as numerical analysis for underground and/or slope design. In this study, the validity of mechanical crack model was checked out by simulating the non-linear behavior of rock and consequently it was applied to a practical numerical analysis, finite element analysis commonly used.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.82-89
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• 2002

The inherent strain method is known to be very effective in predicting the plate deformation by line heating. Traditionally the inherent strain regions have been determined from the temperature distribution and the phase transformation regions(Ac3) of welding experiments. Since the phenomena of line heating are similar to those of welding, the experimental results under the same welding conditions have been applied directly to line heating analysis. The results cannot, however, reflect the effect of heating pattern and plate thickness. Besides, water-cooling in the actual heating process can alter the steel's phase to martensite and shear plastic deformation occurs during the transformation. In this study, the experimental measurement of temperature distribution was substituted with a transient heat transfer analysis using FEM so that we could obtain the temperature distribution according to heat flux models of the heating pass. In order to consider plastic strains occurring additionally under phase transformation, inherent strain regions were assumed to be limited to the eutectoid temperature(Ac1). Using the regions, plate deformations could be predicted to validate our method and the results were in good agreement with the experimental ones

• Steel and Composite Structures
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• v.35 no.1
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• pp.61-76
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• 2020

In this paper, the dynamic behaviour of an inclined functionally graded material (FGM) beam with different boundary conditions under a moving mass is investigated based on the first-order shear deformation theory (FSDT). The material properties vary continuously along the beam thickness based on the power-law distribution. The system of motion equations is derived by using Hamilton's principle. The finite element method (FEM) is adopted to develop a general solution procedure. The moving mass is considered on the top surface of the beam instead of supposing it on the mid-plane. In order to consider the Coriolis, centrifugal accelerations and the friction force, the contact force method is used. Moreover, the effects of boundary conditions, the moving mass velocity and various material distributions are studied. For verification of the present results, a comparative fundamental frequency analysis of an FGM beam is conducted and the dynamic transverse displacements of the homogeneous and FGM beams traversed by a moving mass are compared with those in the existing literature. There is a good accord in all compared cases. In this study for the first time in dynamic analysis of the inclined FGM beams, the Coriolis and centrifugal accelerations of the moving mass are taken into account, and it is observed that these accelerations can be ignored for the low-speeds of the moving mass. The new provided results for dynamics of the inclined FGM beams traversed by a moving mass can be significant for the scientific and engineering community in the area of FGM structures.

• Steel and Composite Structures
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• v.35 no.5
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• pp.659-670
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• 2020

This paper proposes the use of a porous core between layers of laminated composite plates to examine its effect on the natural frequencies of the resulted porous laminated composite sandwich plate (PLCSP) resting on a two-parameter elastic foundation. Moreover, it has been suggested that the dispersion of porosity has two different functionally graded (FG) patterns which are compared with a uniformly dispersed (UD) profile to find their best vibrational efficiency in the proposed PLCSPs. In FG patterns, two types of dispersions, including symmetric (FG-S) and asymmetric (FG-A) patterns have been considered. To derive the governing Eigen value equation of such structures, the first order shear deformation theory (FSDT) of plates has been employed. Accordingly, a finite element method (FEM) is developed to solve the derived Eigen value equation. Using the mentioned theory and method, the effects of porosity parameters, fiber orientation of laminated composite, geometrical dimensions, boundary conditions and elastic foundation on the natural frequencies of the proposed PLCSPs have been studied. It is observed that embedding porosity in core layer leads to a significant improvement in the natural frequencies of PLCSPs. Moreover, the natural frequencies of PLCSPs with FG porous core are higher than those with UD porous core.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.67-74
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• 1999

Self-Boring Pressuremeter Test(SBPT) is known to be the most effective in-situ test method which can reliably determine consolidation characteristics as well as deformation modules and untrained shear strength. In order to derive the coefficient of consolidation using SBPT results it is necessary to obtain the dissipation behavior from the pore pressure change with time during constant radial strain(generally 10%) and to derive the reliable time factor(Τ) from the analytical method which considers the real in-situ conditions. As previous studies on time factor are based on the assumptions of plane strain condition that the membrane of SBP is infinite, of untrained condition during the expansion of the probe and of elastic soil behavior during consolidation, these analyses can't consider the real boundary conditions and the real soil behaviour. In this study, consolidation analysis similar to real in-situ conditions including test procedure is conducted using finite element program which employs MCC model and Biot theory. Time factor considering the effects of finite membrane length, the total pressure change during consolidation and partial drainage is proposed and compared with previous results.

• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.981-995
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• 2015

This paper presents a finite element procedure for dynamic analysis of non-uniform Timoshenko beams made of axially Functionally Graded Material (FGM) under multiple moving point loads. The material properties are assumed to vary continuously in the longitudinal direction according to a predefined power law equation. A beam element, taking the effects of shear deformation and cross-sectional variation into account, is formulated by using exact polynomials derived from the governing differential equations of a uniform homogenous Timoshenko beam element. The dynamic responses of the beams are computed by using the implicit Newmark method. The numerical results show that the dynamic characteristics of the beams are greatly influenced by the number of moving point loads. The effects of the distance between the loads, material non-homogeneity, section profiles as well as aspect ratio on the dynamic responses of the beams are also investigated in detail and highlighted.